The present invention relates to a developing composition and a sheet coated therewith for a pressure-sensitive copy paper, and particularly to a developing composition and a sheet for a pressure-sensitive copy paper in which a reduced degree of yellowing of a developed layer is generated and which exhibits excellent performance in regard to the coloring of colored images and improved weather resistance thereof.
A no-carbon pressure-sensitive copy paper comprises an upper sheet to which are applied micro-capsules each containing a solution of an electron donative colorless dye and a lower sheet to which is applied an electron acceptive developer. When the micro-capsules on the upper sheet are broken by pressure, the colorless dye which flows out reacts with the developer on the lower sheet to obtain a colored image. Examples of developers which have been put into practical use include active clay such as acid clay, p-substituted phenolic novolak resins such as p-phenylphenol novolak resins, and metal salts of aromatic carboxylic acids.
Of these developers, p-substituted phenolic novolak resins, particularly p-phenylphenol novolak resins, have advantages with respect to their excellent performance in terms of coloring and water resistance and the fastness properties of the colored images produced, and are thus frequently used. Such developers have certain disadvantages, however, in that developed layers to tend to yellow during storage in certain atmospheres, and various proposals have previously been put forward with a view to solving this disadvantage.
Examples of such proposals include Japanese Patent Publication No. 29364/1975 in which a resin formed by co-condensation with formaldehyde of p-phenylphenol and phenol substituted by alkyl groups at at least one of the 3- , 4- , and 5-positions is used as a developer composition for a pressure-sensitive copy paper and Japanese Patent Publication No. 4358/1986 in which a resin formed by co-condensation with formaldehyde or p-substituted phenol and phenol having three or more functional groups by any one of various methods is used as a developer composition for a pressure-sensitive copy paper. The use of these developer compositions has ameliorated the problems of yellowing to some extent, but not with completely satisfactory results.
In addition, it is stated in Japanese Patent Publication No. 31678/1985 that a composition formed by uniformly dissolving 1 to 20 parts by weight of a hindered phenol compound in 100 parts by weight of a phenol-formaldehyde polymer may be used as a developer for a pressure-sensitive copy paper. It is also stated in the same publication that the hindered phenol compound may be added at the same time as the addition of raw reaction materials in the reaction for producing the phenol-formaldehyde polymer. However, the condensation reaction between the hindered phenol compound added at the same time as the reaction raw materials and formaldehyde is not described in that same publication, and each of the examples described in the publication in which the hindered phenol compound and the reaction raw materials are added at one time uses a hindered phenol compound which produces substantially no condensation reaction with formaldehyde. In addition, the same publication states that the amount of the hindered phenol compound to be added is as small as 1 to 20 parts by weight relative to 100 parts by weight of a phenolic resin. The use of the developer composition disclosed in the publication still fails to adequately ameliorate the degree of yellowing combining the above-described factors.